Live Aquaria suggests 55g min. Mine cruises constantly in and out of rocks throughout the entire tank. It doesn't bother any other fish in the tank, but now that it's full grown it's started taking out all my shrimp.
You can keep a small one in there, but it will eventually outgrow it. As they can get about 6-8" As long as you are not adding any Fish after it has settled in you should be fine with aggression...just don't give it any Shrimp to eat....lol, as mentioned they will take out all Shrimp eventually.
They get too large, no question. That and they are just not nice fish. Look into Possum Wrasses instead from the Wetmorella genus. I have one in my 28 and it is a very nice sized tank for it.